The rapid expansion in the use of the Internet has resulted in a demand for high speed communications links and devices, including optical links and devices. Optical links using fiber optics have many advantages compared to electrical links: large bandwidth, high noise immunity, reduced power dissipation and minimal crosstalk. Fiber optic communications links can operate with carrier frequencies in the GHz and THz ranges. In communications systems where optical fibers are used to transport optical communications signals, various optoelectronic devices are used to control, modify and process the optical signals. These devices include: modulators, attenuators, switches, beam diverters, tunable filters and other devices.
Integrated optoelectronic devices made of silicon are highly desirable since they can be fabricated in the same foundries used to make VLSI integrated circuits. Optoelectronic devices integrated with their associated electronic circuits can eliminate the need for more expensive hybrid optoelectronic circuits. Optoelectronic devices built using a standard CMOS process are very desirable and the advantages of such devices include: high yields, low fabrication costs and continuous process improvements.